How can I reveal these groups inside of collections in blender 2.9
Click this button and you will get dropdown for restriction tools
Click on monitor looking icon.

Now you can see additional icons  for your objects and collections.
Greyed out object should have monitor icon disabled

Enable the icon to make objects/collection visible again.
Now, you may ask what's the difference between Eye icon and Monitor icon visibility.

Visibility controlled by eye icon is bound to current view layer.
which means it does not affect the visibility of object in other view
layer.

Visibility controlled by Monitor icon is global which means if you
disable it in current view layer then object's visibility in all other view layers are disabled.